Dc-dc converters

Abstract

This application relates to switch mode DC-DC converter circuitry having a power switch operably connected between a supply node and an inductor node. The DC-DC converter has switch control circuitry for driving the power switch which is configured to controllably vary the rate of at least one of turn-on or turn-off of the first power switch. The rate may be based on the operational conditions of the converter, e.g. inductor current, one or more supply voltages and/or operating mode or activity level of a host device. By increasing the rate at which the switch turns-on or off switch transition power losses can be reduced. However a faster switching speed can lead to an increased voltage stress on the circuitry. Embodiments of the present invention varying the rate or turn-on and/or turn-off of the switch to reduce power losses but remain with the safe operating limits for the circuitry.

What is claimed is: 
     
         1 . DC-DC converter circuitry comprising:
 a first supply node for connection to a first voltage supply line;   a second supply node for connection to a second voltage supply line;   an inductor node for connection to an inductor;   a first power switch operably connected between said first supply node and said inductor node; and   switch control circuitry configured to controllably vary the rate of at least one of turn-on or turn-off of the first power switch.   
     
     
         2 . DC-DC converter circuitry as claimed in  claim 1  wherein said switch control circuitry is configured to vary said rate of at least one of turn-on or turn-off of the first power switch based on the operational conditions of the converter. 
     
     
         3 . DC-DC converter circuitry as claimed in  claim 1  wherein said switch control circuitry is configured to vary said rate of at least one of turn-on or turn-off of the first power switch based on at least one of the magnitude and the polarity of current flow out of the inductor node. 
     
     
         4 . DC-DC converter circuitry as claimed in  claim 1  wherein said switch control circuitry is configured to vary said rate of at least one of turn-on or turn-off of the first power switch based on at least one supply voltage of the converter. 
     
     
         5 . DC-DC converter circuitry as claimed in  claim 4  wherein said switch control circuitry is configured to vary said rate of at least one of turn-on or turn-off of the first power switch based on at least one of an input supply voltage; the output supply voltage or the voltage difference between supply voltages of the first and second voltage supply lines. 
     
     
         6 . DC-DC converter circuitry as claimed in  claim 1  wherein said switch control circuitry is configured to vary said rate of at least one of turn-on or turn-off of the first power switch based on an activity level and/or an operating mode of a host system. 
     
     
         7 . DC-DC converter circuitry as claimed in  claim 1  wherein said switch control circuitry comprises a control input for receiving a control signal for setting said rate of turn-on or turn-off of said first power switch. 
     
     
         8 . DC-DC converter circuitry as claimed in  claim 1  further comprising a switch element operably connected between said second supply node and said inductor node. 
     
     
         9 . DC-DC converter circuitry as claimed in  claim 8  wherein said switch element is a second power switch and wherein said switch control circuitry is configured to controllably vary the rate of at least one of turn-on and turn-off of said second power switch. 
     
     
         10 . DC-DC converter circuitry as claimed in  claim 1  operable as a buck converter wherein:
 said first supply node is a high-side input supply node; and 
 said second supply node is a low-side input supply node; 
 wherein said switch control circuitry is configured to controllably vary the rate of turn-off of said first power switch. 
 
     
     
         11 . DC-DC converter circuitry as claimed in  claim 10  wherein said switch control circuitry is configured such that only the rate of turn-off of said first power switch is varied. 
     
     
         12 . DC-DC converter circuitry as claimed in  claim 1  operable as a boost converter wherein:
 said first supply node is a low supply node; and 
 said second supply node is an output voltage supply node; 
 wherein said switch control circuitry is configured to controllably vary the rate of turn-off of said first power switch. 
 
     
     
         13 . DC-DC converter circuitry as claimed in  claim 1  operable as an buck-boost converter wherein:
 said first supply node is a high-side supply voltage; and 
 said second supply node is an output supply node; 
 wherein said switch control circuitry is configured to controllably vary the rate of turn-off of said first power switch. 
 
     
     
         14 . DC-DC converter circuitry as claimed in any of  claim 1  operable as an inverting converter wherein:
 said first supply node is a high-side input supply voltage; and 
 said second supply node is an output supply node; 
 wherein said switch control circuitry is configured to controllably vary the rate of turn-off of said first power switch. 
 
     
     
         15 . DC-DC converter circuitry as claimed in  claim 1  wherein said switch control circuitry comprises:
 at least a first pre-driver having a variable drive strength; and 
 pre-driver control circuitry for controlling the drive strength of said first pre-driver. 
 
     
     
         16 . DC-DC converter circuitry as claimed in  claim 15  where said first pre-driver has a variable resistance and said pre-driver control circuitry controls said variable resistance. 
     
     
         17 . DC-DC converter circuitry as claimed in  claim 15  wherein said first-pre-driver has a variable maximum current output and said pre-driver control circuitry controls said maximum current output. 
     
     
         18 . DC-DC converter circuitry as claimed in  claim 15  wherein said first pre-driver comprises a plurality of parallel driver stages wherein the number of driver stages that contribute to the driver strength is selectable by said pre-driver control circuitry. 
     
     
         19 . DC-DC converter circuitry as claimed in  claim 18  wherein said plurality of driver stages have different driver strengths. 
     
     
         20 . DC-DC converter circuitry as claimed in  claim 1  wherein said switch control circuitry comprises at least one input for receiving at least one of a current signal indicative of current flow out of said inductor node and a voltage signal indicative of a supply voltage of the converter. 
     
     
         21 . DC-DC converter circuitry as claimed in  claim 20  wherein said switch control circuitry is configured to reduce said rate of at least one of turn-on and turn-off of said first power switch at relatively higher current flow out of said inductor node. 
     
     
         22 . DC-DC converter circuitry as claimed in  claim 20  wherein said switch control circuitry is configured to compare at least one of said current signal and said voltage signal with at least one threshold and control said rate of at least one of turn-on and turn-off of said first power based on said comparison. 
     
     
         23 . DC-DC converter circuitry as claimed in  claim 20  wherein said switch control circuitry comprises:
 inputs for receiving both said current signal and said voltage signal; and 
 combining circuitry for producing a combined value wherein said rate of at least one of turn-on and turn-off of said first power switch is based on said combined value. 
 
     
     
         24 . DC-DC converter circuitry as claimed in  claim 23  wherein said combined value is substantially proportional to the value of the current signal and substantially inversely proportional to a constant minus the value of said voltage signal. 
     
     
         25 . DC-DC converter circuitry as claimed in  claim 1  wherein said switch control circuitry comprises:
 an input for receiving an activity signal indicating the activity level of the host system or a signal indicating an operating mode of the host system. 
 
     
     
         26 . DC-DC converter circuitry as claimed in  claim 25  where said activity signal indicates the processing speed of a system processor. 
     
     
         27 . DC-DC converter circuitry as claimed in  claim 25  wherein said switch control circuitry is configured, in response to said activity signal indicating a change in operating conditions, to set the rate of turn-on and/or turn-off of said first power switch to a default level for a period of time. 
     
     
         28 . DC-DC converter circuitry as claimed in  claim 1  wherein said switch control circuitry is configured to set the rate of turn-on and/or turn-off of said first power switch to a default level in the absence of an indication of the operational conditions of the converter. 
     
     
         29 . A power management circuit comprising a DC-DC converter as claimed in  claim 1 . 
     
     
         30 . A device comprising a power management circuit as claimed in  claim 29 . 
     
     
         31 . A device as claimed in  claim 30  wherein the device is at least one of: a portable device; a battery powered device; a mobile telephone; an audio player, a video player; a personal data assistant; a mobile computing platform; a mobile games device; a video player. 
     
     
         32 . A method of reducing power loss in a DC-DC converter having at least one power switch, the method comprising the steps of
 varying the rate of at least one of turn-on and turn-off for at least one power switch.   
     
     
         33 . DC-DC converter circuitry comprising:
 at least one power switch;   pre-driver circuitry for driving said at least one power switch wherein   
       the pre-driver circuitry is configured such that the speed of at least one switch transition of said at least one power switch is controlled based on the operational conditions of the converter. 
     
     
         34 . DC-DC converter circuitry comprising:
 at least one power switch; and   switch control circuitry for driving said at least one power switch wherein:   the switch control circuitry is configured such that the rate of at least one of turn-on or turn-off of said at least one power switch is controlled based on a voltage induced across said switch during said turn-on or turn-off.   
     
     
         35 . DC-DC converter circuitry comprising:
 at least one power switch;   pre-driver circuitry configured to drive said at least one power switch;   wherein the pre-driver circuitry comprises a control input for altering the pre-driver drive strength.   
     
     
         36 . Pre-driver circuitry for driving a power switch wherein the pre-driver circuitry has a drive strength that can be varied in use so as to vary the rate of at least one of turn-on and turn-off of the power switch. 
     
     
         37 . DC-DC converter circuitry comprising:
 a first node for connection to a supply voltage;   a second node for connection to a supply voltage;   a third node for connection to an inductor;   a power switch operably connected between said third node and one of said first node and said second node, said power switch having a control input; and   a switch controller having a drive output connected to said power switch control input;   wherein:
 said switch controller has a control input terminal; and 
 the rate of turn-on or turn-off of the power switch is dependent on a control signal received at said switch controller control input terminal.